Plastic container

ABSTRACT

Disclosed is a plastic container having a wall comprising a layer made of a composition comprising a major amount of crystalline propylene-ethylene-butene-1 copolymer which has specific structural unit proportions and a specific melt flow rate and a minor amount of ethylene-α-olefin copolymer which has specific structural unit proportions, a specific melt flow rate and a specific density, the container being superior in flexibility, impact strength at low temperatures anddurability.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to plastic containers.

2. Description of the Related Art

Containers made of polypropylene resin are superior in many characteristics such as heat resistance, rigidity, chemical resistance and water vapor barrier property and therefore are used in awide variety of applications. However, the containers have a problem of being poor in transparency and many proposals for improving their transparency have been made.

For example, a container obtained by use of a resin composition containing a composition comprising from 98 to 70% by weight of propylene-ethylene random copolymer resin and from 2 to 30% by weight of ethylene-hexene-1 copolymer resin polymerized using a metallocene catalyst and from 0.02 to 1.0 part by weight, based on 100 parts by weight of the composition, ofahigherfattyacidderivative is known (see JP-A-2001-181455). The container has an improved transparency. However, when it is subjected to heat treatment, the higher fatty acid derivative contained in the container migrates to the surface of the container, reducing the transparency or making the surface sticky. Therefore, still some room for improvement is left.

On the other hand, known is a container made of resin comprising a crystalline propylene copolymer having a melt flow rate measured at 230° C of from 0.3 to 8 g/10 min, a propylene content of from 82 to 96.5% by weight, an ethylene content of from 3 to 8% by weight and a content of α-olefin having 4 or more carbon atoms of from 0.5 to 10% by weight and a crystalline ethylene copolymer having a melt flow rate measured at 190° C. of from 0.3 to 50 g/10 min and a density of from 900 to 935 kg/m³, wherein the crystalline ethylene copolymer is blended in an amount of from 4 to 0.05% by weight based on the crystalline propylene copolymer (see JP-A-8-47980). However, it is not sufficient in transparency.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a plastic container which is flexible and is superior in impact strength at low temperatures and which causes a small decrease in transparency and do not get very sticky even when it is subjected to heat treatment.

The present invention provides a plastic container having a wall comprising a layer made of a composition comprising from 70 to 99 parts by weight of a crystalline propylene-ethylene-butene-1 copolymer having features [1] and [2] defined below and from 1 to 30 parts by weight of an ethylene-α-olefin copolymer having features [3, [4] and [5], where the combined amount of both copolymers is 100 parts by weight:

[1] to have a content of propylene-derived structural units of from 70 to 97% by weight, a content of ethylene-derived structural units of from 1 to 10% by weight and a content of butene-1-derived structural units of from 2 to 20% by weight,

[2] to have a melt flow rate, measured at a temperature of 230° C. and a load of 2.16 kgf, of from 1 to 10 g/10 min,

[3] to be a copolymer of ethylene and an α-olefin having from 4 to 12 carbon atoms, the copolymer having a content of ethylene-derived structural units of 50% by weight or more,

[4] to have a melt flow rate, measured at a temperature of 190° C. and a load of 2.16 kgf, of from 0.1 to 50 g/10 min, and

[5] to have a density of from 865 to 898 kg/m³.

A first embodiment of the present invention is directed to a plastic container having a wall composed of a single layer made of the composition comprising from 70 to 99 parts by weight of the crystalline propylene-ethylene-butene-1 copolymer having the features [1] and [2] defined above and from 1 to 30 parts by weight of the ethylene-α-olefin copolymer having the features [3], [4] and [5] defined above, wherein the combined amount of both copolymers is 100 parts by weight.

A second embodiment of the present invention is directed to a plastic container having a wall composed of two or more layers including at least one layer made of the composition comprising from 70 to 99 parts by weight of the crystalline propylene-ethylene-butene-1 copolymer having the features [1] and [2] defined above and from 1 to 30 parts by weight of the ethylene-α-olefin copolymer having the features [3], [4] and [5] defined above, wherein the combined amount of both copolymers is 100 parts by weight.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a container produced in Example 1 using the third-angle projection.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The essential composition used in the plastic containers of the present invention contains, as constituents, acrystalline propylene-ethylene-butene-1 copolymer having the features [1] and [2] defined below and an ethylene-α-olefin copolymer having the features [3], [4] and [5] defined below.

The propylene-ethylene-butene-1 copolymer used in the present invention is acrystalline copolymermade up of propylene, ethylene and butene-1, the copolymer containing from 70 to 97% by weight of propylene-derived structural units, from 1 to 10% by weight of ethylene-derived structural units and from 2 to 20% by weight of butene-1-derived structural units. In the present invention, a crystalline polymer refers to a polymer whose heat of fusion measured by a differential scanning calorimeter is 20 J/g or more. The heat of fusion of the ethylene-propylene-butene-1 copolymer used in the present invention is preferably from 20 to 100 J/g, more preferably from 25 to 90 J/g, and particularly preferably from 30 to 80 J/g. In the present invention, the heat of fusion of a polymer is determined according to the following procedure. First, a crystal fusion curve is produced according to the following procedure using a differential scanning calorimeter DSC-VII manufactured by PerkinElmer, Inc. or a measuring instrument equivalent to this. The heat of fusion (J/g) is calculated from the area of a portion surrounded by the resulting crystal fusion curve and its baseline.

(1) A sheet 65 mm in diameter and 100 μm in thickness is prepared by compression molding at a temperature of 230° C.

(2) A test piece is prepared by punching the sheet produced in step (1) into a diameter of 5 mm by means of a punching machine.

The test piece is weighed on an electronic balance.

(3) The test piece prepared in step (2) is put into a sample pan.

(4) The test piece in the sample pan is applied with the thermal hysteresis shown below under a nitrogen atmosphere:

(i) the test piece is heated from 24° C. to 220° C. at a rate of 300° C./min,

(ii) after the heating (i), the test piece is held at 220° C. for five minutes,

(iii) after the step (ii), the test piece is cooled to 150° C. at a rate of 300° C./min,

(iv) after the cooling (iii), the test piece is held at 150° C. for one minute,

(v) after the step (iv), the test piece is cooled to 50° C. at a rate of 5° C./min,

(vi) after the cooling (v), the test piece is held at 50° C. for one minute, and (vii) after the step (vi), the test piece is heated to 180° C. at a rate of 5° C./min.

In the present invention, a single kind of or two or more kinds of propylene-ethylene-butene-1 copolymers are used. For example, two or more kinds of copolymers differing in molecular weight may be employed. Alternatively, two or more kinds of copolymers differing in contents of the three kinds of structural units may be used.

For the propylene-ethylene-butene-1 copolymer having the features [1] and [2], it is desirable to have a content of ethylene-derived structural unit of from 1.3 to 8% by weight and a content of butene-1-derived structural units of from 2.5 to 15% by weight. It is more desirable for the copolymer to have a content of ethylene-derived structural unit of from 1.5 to 5% by weight and a content of butene-l-derived structural units of from 3 to 12% by weight. It is particularly desirable for the copolymer to have a content of ethylene-derived structural unit of from 2 to 3% by weight and a content of butene-1-derived structural units of from 4 to 10% by weight. If the content of ethylene-derived structural units is less than 1% byweight or the content of butene-1-derived structural units is less than 2% by weight, containers will be poor in flexibility. If the content of ethylene-derived structural units is more than 10% byweight or the content of butene-1-derived structural units is more than 20% by weight, the container will be poor in heat resistance.

The combined content of the ethylene-derived structural units and the butene-1-derived structural units in the propylene-ethylene-butene-lcopolymerisfrom3 to30%byweight, preferably from 3.8 to 23% by weight, and more preferably from 4.5 to 17% by weight. If the combined content is less than 3% by weight, the container tends to be poor in flexibility, whereas if more than 30% by weight, containers tend to be poor in heat resistance.

The propylene-ethylene-butene-1 copolymer preferably is a copolymer satisfying formula (1) below. If formula (1) is satisfied, containers tend to have particularly favorable heat resistance. Thepropylene-ethylene-butene-lcopolymerismore preferably a copolymer satisfying formula (2) below, and even more preferably is a copolymer satisfying formula (3) below: x+1<y  (1) x+2<y  (2) x+3<y  (3) wherein x denotes a content (% by weight) of ethylene-derived structural units and y denotes a content (% by weight) of butene-1-derived structural units.

Thepropylene-ethylene-butene-1-copolymerhasameltflow rate measured at a temperature of 230° C. and a load of 2.16 kgf (henceforth referred to as MFR(230° C., 2.16 kgf)) is from 1 to 10 g/lO min, preferably from 1.5 to 8 g/lomin, and more preferably from 2 to 6 g/10 min. If MFR(230° C., 2.16 kgf) is less than 1 g/10 min, the surface of containers is roughened during their molding, leading to decrease in transparency. If MFR(230° C., 2.16 kgf) is over 10 g/10 min, the impact strength at low temperatures of containers becomes poor and the flexibility of containers is affected.

The content of the propylene-ethylene-butene-1 copolymer in the composition is from 70 to 99 parts by weight, preferably from 75 to 97 parts by weight, more preferably from 80 to 96 parts by weight, and particularly preferably from 82 to 95 parts by weight, wherein the combined amount of the propylene-ethylene-butene-1 copolymer and the ethylene-α-olefin copolymer mentioned later is 100 parts by weight. If the amount of the propylene-ethylene-butene-1 copolymer is less than 70 parts by weight, the heat resistance of containers becomes poor. If the amount of the propylene-ethylene-butene-1 copolymer is more than 99 parts by weight, the impact strength at low temperatures of containers becomes insufficient.

The method for producing the propylene-ethylene-butene-1 copolymer may be a method in which propylene, ethylene and butene-1 are polymerized in the presence of a polymerization catalyst comprising a transition metal compound, which method is disclosed in JP-A-11-228629. The polymerization of the monomers may be, for example, solution polymerization, bulk polymerization and gas phase polymerization. The monomers may be polymerized by a single polymerization technique or alternatively by a multistage polymerization composed of these polymerization methods in combination. From the viewpoint of production cost, use of gas phase polymerization is preferred.

The ethylene-α-olefin copolymer refers to a copolymer of ethylene and an α-olefin having from 4 to 12 carbon atoms, which copolymer contains at least 50% by weight of ethylene-derived structural units. The content of ethylene-derived structural units is preferably up to 55% by weight, more preferably up to 60% by weight, and even more preferably up to 65% by weight. Examples of the α-olefin include butene-1, 4-methylpentene-1, hexene-1, octene-1 and decene-1. Preferable α-olefin includes butene-1and hexene-1. The ethylene-α-olefin copolymer (B) may be a mixture of two or more ethylene-α-olefin copolymers differing in molecular weight or in kind and content of α-olefin.

The amount of the α-olefin having from 4 to 12 carbon atoms is ordinarily 5% by weight or more, preferably 8% by weight or more, and more preferably 10% by weight or more.

The ethylene-α-olefin copolymer has a melt flow rate measured at a temperature of 190° C. and a load of 2.16 kgf (henceforth, referred to as MFR(190° C., 2.16 kgf)) of from 0.1 to 50g/lomin, preferably from0.5 to 40 g/lomin, morepreferably from 1 to 30 g/10 min, and even more preferably from 2 to 20 g/10 min.

If MFR (190° C., 2.16 kgf) is less than 0.1 g/10 min, dispersed particles of the ethylene-α-olefin copolymer in containers become coarse, resulting in poor transparency of containers. If MFR(190° C., 2.16 kgf) is over 50 g/10 min, the impact strength at low temperatures of containers becomes insufficient.

The density of the ethylene-α-olefin copolymer is from 865 to 898 kg/m³, preferably from 868 to 897 kg/m³, and more preferably from 870 to 896 kg/m³.

If the density is less than 865 kg m³, the density difference between the ethylene-α-olefin copolymer and the propylene-ethylene-butene-1 copolymer becomes large and the transparency of containers becomes poor. Also if the density is over 898 kg/m³, the density difference between the ethylene-α-olefin copolymer and the propylene-ethylene-butene-1 copolymer becomes large and the transparency of containers becomes poor.

The method for producing the ethylene-α-olefin copolymer may be a method in which ethylene and α-olefin are polymerized in the presence of a catalyst (metallocene catalyst) containing a transition metal compound comprising a group having a cyclopentadiene-type anion skeleton, which method is disclosed in JP-A-3-234717. The polymerization of the monomers may be known polymerization methods, for example, solution polymerization, slurry polymerization, gas phase polymerization and high-pressure ion polymerization.

The essential composition used in the plastic containers of the present invention may contain a crystalline propylene-ethylene copolymer containing at least 90% by weight of propylene-derived structural units and a crystalline propylene-butene-1 copolymer containing at least 65% by weight of propylene-derived structural units, unless the effect of the present invention is affected.

The addition of a propylene-ethylene copolymer or propylene-butene-1 copolymer having a low MFR improves the impact strength at low temperatures of containers. Addition of a propylene-ethylene copolymer or propylene-butene-1 copolymer having a high MFR improves the transparency of containers.

The combined content of the propylene-ethylene copolymer andthepropylene-butene-1 copolymerbasedon 100 parts byweight of the propylene-ethylene-butene-1 copolymer and the ethylene-α-olefin in total is up to 30 parts byweight, preferably up to 25 parts by weight, and more preferably up to 20 parts by weight.

The content of ethylene-derived structural units in the propylene-ethylene copolymer is preferably from 3 to 10% by weight, more preferably from 3.5 to 8% by weight, and even more preferably from 4 to 7% by weight. If the content of ethylene-derived structural units is less than 3% by weight, containers tend to be poor in flexibility. If over 10% byweight, containers tend to be poor in heat resistance.

The content of butene-1-derived structural units in the propylene-butene-1 copolymer is preferably from 3 to 35% by weight, more preferably from 4 to 30% by weight, and even more preferably from 5 to 25% by weight. If the content of butene-1-derived structural units is less than 3% by weight, containers tend to be poor in flexibility. If over 35% byweight, containers tend to be poor in heat resistance.

The propylene-ethylene copolymer and the propylene-butene-1 copolymer has an MFR(230° C., 2.16 kgf) of from 0.1 to 100 g/10 min, preferably from 0.3 to 50 g/10 min, and more preferably from 0.5 to 30 g/10 min. If MFR(230° C., 2.16 kgf) is less than 0.1 g/10 min, the surface of a container is roughened during its molding, leading to decrease in transparency. MFR(230° C., 2.16 kgf) over 100 g/10 min results in a poor workability for molding a container and containers will have a poor impact strength at low temperatures.

The methods for producing the propylene-ethylene copolymer and the propylene-butene-1 may be, for example, a method in which monomers are polymerized in the presence of a polymerization catalyst comprising a transition metal compound, which method is disclosed in JP-A-11-228629. The polymerization of the monomers may be, for example, solution polymerization, bulk polymerization and gas phase polymerization. The monomers may be polymerized by a single polymerization technique or alternatively by a multistage polymerization composed of these polymerization methods in combination. From the viewpoint of production cost, use of gas phase polymerization is preferred.

The composition containing the propylene-ethylene-butene-1 copolymer and the ethylene-α-olefin copolymer may contain, in addition to the propylene-ethylene-butene-1 copolymer and the ethylene-α-olefin copolymer, additives such as talc, calcium carbonate, mica, glass fiber, carbonfiber, neutralizingagents, antioxidants, thermal stabilizers, weathering agents, lubricants, UV absorbers, antistatic agents, antiblocking agents, anticlouding agents, antifoaming agents, dispersing agents, antifungus agents, fluorescent whitening agents, dyestuff and pigment, unless the effect of the present invention is affected.

The combined amount of the additives is from 0.001 to 5 parts by weight based on total 100 parts by weight of the combined amount of the propylene-ethylene-butene-1 copolymer and the ethylene-α-olefin copolymer.

In one embodiment of the present invention, a plastic container has a wall composed of a single layer made of the composition comprising from 70 to 99 parts by weight of the crystalline propylene-ethylene-butene-1 copolymer having the features [1] and [2] defined above and from 1 to 30 parts by weight of the ethylene-α-olefin copolymer having the features [3], [4] and [5] defined above, wherein the combined amount of both copolymers is 100 parts by weight. In this case, the thickness of the layer of the composition may be determined appropriately depending on the application of the container and is not particularly limited.

Another embodiment of the present invention is directed to a multilayer plastic container having a wall composed of two or more layers including at least one layer made of the composition. Examples of the material which constitutes the layer or layers other than the layer of the composition include ethylene-vinyl alcohol copolymer, polyamide resin and polyethylene terephthalate resin. Moreover, a composition prepared by recycling flashes generated during the molding of plastic containers of the present invention may be used. In the multilayer plastic container, the thickness of the wall may be determined appropriately depending on the application of the container and is not particularly limited. The thickness of the layer made of the essential composition is preferably 30% or more, more preferably 40% or more, and particularly preferably 50% or more of the whole thickness of the wall.

The method for producing the containers of the present invention will be explained below. It should be noted that although the method for producing containers having a wall composed of a single layer made of the essential composition will mainly be described, multilayer containers can also be produced by application of the following teachings to multilayer molding techniques using multilayer molding machines.

The container of the present invention can be obtained by mixing a propylene-ethylene-butene-1 copolymer, an ethylene-α-olefin copolymer and, if desired, other components to yield a mixture, kneading the mixture to yield a composition, and molding the composition.

The method for mixing a propylene-ethylene-butene-1 copolymer, anethylene-α-olefin copolymer and, if desired, other components is not particularly restricted. For example, a method comprising mixing the components by means of a conventional mixing machine may be used.

Examples of the mixing machine include a Henschel mixer (trade name), a Super mixer (trade name), a ribbon blender and a tumbler.

The method for kneading the mixture resulting from the mixing of a propylene-ethylene-butene-1 copolymer, an ethylene-α-olefin copolymer and, if desired, other components is not particularly restricted. For example, a method comprising kneading the components by means of a conventional kneading machine. Examples of the kneading machine include a single screw extruder, amultiple screw extruder, a Banbury mixer, a kneader and a roll mill. The mixing machine and the kneading machine may be connected to a machine for molding containers.

The conditions for the kneading are not particularly restricted unless the molten resin is significantly degraded from shear stress, externally-applied heat and shear heat generation during the kneading and a long residence of the resin in the kneading machine or an insufficient and uneven dispersion state is formed.

Examples of the method for molding containers of the present invention include injection molding, compression molding, injection compression molding, pressure molding, vacuum molding, extrusion blow molding, injection blow molding and injection stretch blow molding.

Of these techniques, extrusion blow molding, injection blow molding and injection stretch blow molding are preferable, and extrusion blow molding is especially preferable. Containers produced by extrusion blow molding are particularly desirable because they are superior in flexibility, transparency, impact strength at low temperatures, and heat resistance.

For the production of plastic containers of the present invention, conventional blow molding machines may be used. Ablow molding machine has, for example, a section where aparison is formed by continuously or intermittently extruding, through a die, a plasticated composition kneaded in an extruder, a mold having a cavity with a product shape and a device for blowing compressed gas into the mold cavity. Available are a reciprocating type extrusion blow molding machine in which a mold reciprocates between the extruder and the blowing machine and a rotary type extrusion blow molding machine in which two or more molds are arranged on a vertical or horizontal circular orbital and the molds are rotated continuously.

The outline of the method for producing a plastic container of the present invention using an extrusion blow molding machine is described below.

The raw material charged into an extruder is melted and kneaded in the cylinder of the extruder, and then extruded through a gap between a die and a core mounted at one end of the extruder, forming a tubular parison. The extruded parison is trapped between mold halves which are combined to define acavity together. Then, compressed gas is blown into the parison. The parison is formed into the shape of the mold cavity by the action of the compressed gas, and then cooled. Subsequently, the mold halves are opened and a resulting container is ejected.

One preferred method of extrusion blow molding is described below.

For melt kneading the raw materials, a single screw, combined screws, a gear pump, or the like may be employed. Parisons may be extruded either continuously or intermittently. The shape and material of a die and a core for forming parisons and the gap between the die and the core are not particularly restricted. For preventing an extruded parison from draw-down or making the parison have a thickness distribution suitable for an intended blow-up ratio, the thickness of the parison may be controlled by means of a parison controller. One may blow compressed gas into a parison during the extrusion of the parison. One may pinch-off a bottom of an extruded parison and then blow compression air into the parison.

There are no particular limitations on resin temperature, mold temperature, kind of compressed gas, blowing pressure and blowing time unless the effect of the present invention is affected.

The plastic containers of the present invention include the composition containing the specific propylene-ethylene-butene-1 copolymer and the specific ethylene-α-olefin copolymer as described above. Therefore, the containers are superior in impact strength, flexibility and transparency and release less odor. In addition, they exhibit less reduction in transparency and their surfaces do not get very sticky when they are subjected to heat treatment. Consequently, they are available for a wide variety of applications, e.g. liquid packaging containers, food packaging containers, medical containers, automotive appliances, home electrical appliances, industrial products and sundries. Especially, they can be employed suitably as medical containers, such as containers for containing and transporting drug solutions such as solutions of blood components, physiological saline solution, electrolyte, dextran preparations, mannitol preparation, saccharide preparations, amino acid preparations and lipid microspheres.

EXAMPLES

The present invention will be further described by referring to examples below. However, the invention is not restricted to the examples.

Evaluation methods used in the examples and comparative examples are as follows.

1. Melt Flow Rate (MFR)

MFRs (g/10 min) of propylene-ethylene-butene-1 copolymers and propylene-ethylene copolymers were measured at 230° C. according to JIS K 7210, Condition 14. MFR (g/10 min) of resin compositions was measured under the same conditions as above. MFR (g/10 min) of ethylene-α-olefin copolymers was measured at 190° C. according to JIS K 6760.

2. Density (d)

Density (kg/m³) of polymers was measured according to JIS K 6760-1981.

3. Flexural Modulus (FM)

Flexural modulus (MPa) of compression molded sheets was measured according to JIS K 7106.

4. IZOD Impact Strength (Izod)

A test piece with a V notch was prepared according to JIS K 7110. After being allowed to stand in a thermostat at 0° C. for 24 hours or longer, the test piece was measured for IZOD impact strength (kJ/m²).

5. Haze and Transmittance

Haze (%) and transmittance (%) of a 1 mm thick compression molded sheet prepared according to JIS K 6758 were measured according to JIS K 7105.

6. Drop Strength of Container

A container was filled with 500 g of water and a polypropylene cap was fitted thereto. After being allowed to stand in a thermostat at 5° C. for 24 hours or longer, the container was dropped freely from a height of 1.2 m onto a concrete floor ten times repeatedly with the body of the container down. After the ten drops, the condition of the container was observed. Ten test bottles of the same structure were subjected to the same test. The ratio (%) of the number of unbroken bottles to the number of the whole bottles tested was used as the drop strength of bottles of that structure.

7. Haze and Transmittance of Container

A test piece was prepared by cutting out a central portion of a container. Haze (%) and transmittance (%) of the test piece were measured according to JIS K 7105.

8. Heat Resistance of Container

A container was hung using a hanger formed on the bottom of the container and was allowed to stand in a thermostatic chamber at 121° C. for 20 minutes. Thereafter, it was cooled to room temperature and a central portion of the sidewall of the container was cut out. Thus, a test piece was prepared. Haze (%) and transmittance (%) of the test piece were measured according to JIS K 7105.

9. Stickiness of Container

A container was hung using a hanger formed on the bottom of the container and was allowed to stand in a thermostatic chamber at 121° C. for 20 minutes. Thereafter, it was cooled at ambient temperature for 24 hours and then two test pieces were prepared by cutting a central portion of the body of the container into rectangles each sized 225 mm in a longitudinal direction and 50 mm in a transverse direction. The two pieces were laminated together on their outer surfaces and was allowed to stand in a thermostat at 60° C. for three hours with a 9.5-kg weight having a bottom sized 225 mm by 50 mm thereon. The lower test piece was fixed and the upper test piece was held with a chuck at its one end. The upper test piece was pulled up while the tensile load was increased at a rate of 20 gf/min. A tensile load (gf/100 cm²) at the time the test pieces peeled off was recorded. The larger the tensile load, the more the stickiness.

10. Heat of Fusion

Using a differential scanning calorimeter DSC-VII manufactured by Perkin Elmer, Inc., a crystal melting curve of a polymer was produced in the procedure described previously and then a heat of fusion (J/g) was calculated.

The polymers used in examples and comparative examples are as follows.

1. Propylene-Ethylene-Butene-1 Copolymer

Propylene-Ethylene-Butene-1 Copolymer (1):

MFR(230° C., 2.16 kgf) was 3.8 g/10 min. The content of ethylene-derived structural units and that of butene-1-derived structural units were 2.4% by weight and 6.8% by weight, respectively. The heat of fusion measured by a differential scanning calorimeter was 70.9 J/g.

2. Propylene-Ethylene Copolymer

Propylene-Ethylene copolymer (1):

MFR(230° C., 2.16 kgf) was 1.5 g/10 min. The content of ethylene-derived structural units was 5.6% by weight. Propylene-ethylene copolymer (2):

3. Ethylene-α-Olefin Copolymer

Ethylene-α-Olefin Copolymer (1):

An ethylene-hexene-1 copolymer named Excellen FX CX2001 manufactured by Sumitomo Chemical Co., Ltd. This is a copolymer produced in the presence of a metallocene catalyst. It has an MFR(19OdegC., 2.16 kgf) of 2.0 g/10 min and a density of 896 kg/m³.

Ethylene-α-Olefin Copolymer (2):

An ethylene-hexene-1 copolymer named Excellen FX CX4002 manufactured by Sumitomo Chemical Co., Ltd. This is a copolymer produced in the presence of a metallocene catalyst. It has an MFR(190° C., 2.16 kgf) of 8.0 g/10 min and a density of 883 kg/m³.

Ethylene-α-Olefin Copolymer (3):

An ethylene-hexene-1 copolymer named Excellen FX CX5007 manufactured by Sumitomo Chemical Co., Ltd. This is a copolymer produced in the presence of a metallocene catalyst. It has an MFR(190° C., 2.16 kgf) of 17.7 g/10 min and a density of 875 kg/m³.

Ethylene-α-Olefin Copolymer (4):

An ethylene-butene-1 copolymer named Excellen VL VL100 manufactured by Sumitomo Chemical Co., Ltd. This is a copolymer produced in the presence of a Ti-Mg catalyst. It has an MFR (190° C., 2.16 kgf) of 0.8 g/10 min and a density of 900 kg/m³.

Ethylene-α-Olefin Copolymer (5):

An ethylene-butene-1 copolymer named Sumikathene-L FS250A manufactured by Sumitomo Chemical Co., Ltd. This is a copolymer produced in the presence of a Ti-Mg catalyst. It has an MFR(190° C., 2.16 kgf) of 1.8 g/10 min and a density of 922 kg/m³.

Example 1

Ninety-four parts by weight of propylene-ethylene-butene-1copolymer (1) and 6 parts by weight of ethylene-α-olefin copolymer (1) were blended and then 0.01 part by weight of hydrotalcite DHT-4C (manufactured by Kyowa Chemical Industry Co., Ltd.) and 0.1 part by weight of Irganox B220 (manufactured by Ciba Specialty Chemicals) were added and mixed in a Henschel mixer. The resulting mixture was melt-kneaded in a single screw extruder having a full flight type screw 40 mm in diameter, at a temperature of 230° C. and a screw rotation speed of 100 rpm. Thus, a resin composition was obtained. The resin composition had an MFR of 3.9 g/10 min. The blend proportions of the copolymers and the MFR of the composition are shown in Table 1. Moreover, a compression molded sheet made of the resin composition had a flexural modulus of 760 MPa, an Izod impact strength of 3.5 kJ/m², a transmittance of 89.1% and a haze of 33.6%. The sheet was superior in flexibility, impact strength at low temperatures and transparency. The physical properties of the compression molded sheet are summarized in Table 3.

The resin composition was extruded to form a hot parison at an extrusion rate of 5 kg/h at a die and core temperatures of 210° C. using a blow molding machine NB3B manufactured by The Japan Steel Works, Ltd. having a full flight type screw 50 mm in diameter. The hot parison was trapped between molds controlled to 14° C. and compressed air having a pressure of 0.3 MPa was blow into the parison for 20 seconds. Thus, a container with a hanger on its bottom, the container having a weight of 28 g, a side wall thickness of about 0.4 mm, a capacity of 600 ml and a shape shown in FIG. 1 was produced. The container had a transmittance of 91.8%, a haze of 3.5%, a transmittance and haze after heat treatment of 90.4% and 8.4%, and a peel load of 25.6 g/100 cm2. The container was superior in flexibility, transparency, heat resistance and sanitariness. Physical properties of hollow container is shown for table 4.

Examples 2 to 6

In the same manner as Example 1, resin compositions were obtained by melt-kneading copolymers selected from propylene-ethylene-butene-1 copolymers and ethylene-α-olefin copolymers in a blend proportions given in Table 1. Moreover, containers were also produced in the same manner as Example 1. The physical properties of the resin compositions and those of the containers made from the compositions are summarized in Table 3 and Table 4, respectively. These containers were superior in flexibility, transparency and heat resistance and exhibited less stickiness.

Comparative Examples 1 to 7

In the same manner as Example 1, resin compositions were obtained by melt-kneading copolymers selected from propylene-ethylene-butene-1 copolymers and ethylene-α-olefin copolymers in a blend proportions given in Table 2. Moreover, a container was also produced in the same manner as Example 1. The physical properties of the resin compositions and those of the containers made from the compositions are summarized in table 3 and Table 4, respectively. These containers were superior in flexibility, but were poor in impact strength, transparency and degree of stickiness. TABLE 1 Example 1 2 3 4 5 6 Propylene-ethylene-butene-1 block copolymer Propylene-ethylene-butene-1 94 94 90 80 94 84 block copolymer (1) Propylene-ethylene copolymer Propylene-ethylene copolymer (1) — — — — — 10 Ethylene-α-olefin copolymer Ethylene-α-olefin copolymer (1)  6 — — — — — Ethylene-α-olefin copolymer (2) —  6 10 20 —  6 Ethylene-α-olefin copolymer (3) — — — —  6 — Ethylene-α-olefin copolymer (4) — — — — — — Ethylene-α-olefin copolymer (5) — — — — — — MFR (g/10) of composition   3.9   4.2   4.4   5.1   4.4   3.7

TABLE 2 Comparative Example 1 2 3 4 5 6 Propylene-ethylene-butene-1 block copolymer Propylene-ethylene-butene-1 100 50 90 90 — — block copolymer (1) Propylene-ethylene copolymer Propylene-ethylene copolymer (1) — — — — 100 94 Propylene-ethylene copolymer (2) — — — — — — Ethylene-α-olefin copolymer Ethylene-α-olefin copolymer (1) — — — — — — Ethylene-α-olefin copolymer (2) — 50 — — —  6 Ethylene-α-olefin copolymer (3) — — — — — — Ethylene-α-olefin copolymer (4) — — 10 — — — Ethylene-α-olefin copolymer (5) — — — 10 — — MFR (g/10) of composition    3.8   8.8   3.4   3.7    1.5   1.8

TABLE 3 Physical properties of compression molded sheet Izod Transmittance FM (MPa) (kJ/m²) (%) Haze (%) Example 1 760 3.5 89.1 33.6 Example 2 630 3.4 89.7 31.3 Example 3 760 4.1 91.2 32.0 Example 4 470 7.6 93.3 31.5 Example 5 750 3.0 88.8 31.5 Example 6 640 3.4 88.5 33.7 Comparative 790 1.8 86.2 38.1 Example 1 Comparative 200 27.4 88.8 55.0 Example 2 Comparative 690 3.3 87.2 42.3 Example 3 Comparative 710 2.5 85.1 40.6 Example 4 Comparative 630 3.0 88.0 35.3 Example 5 Comparative 620 3.3 88.9 34.2 Example 6

TABLE 4 Physical properties of container Non-heat treatment After heat treatment Fall Trans- Trans- Peel load strength mittance Haze mittance Haze (g/100 (%) (%) (%) (%) (%) cm²) Example 1 80 91.8 3.5 90.4 8.4 25.6 Example 2 80 92.2 2.2 91.2 6.6 30.6 Example 3 90 91.7 4.3 90.9 8.2 29.6 Example 4 100 90.1 6.4 89.9 12.2 41.2 Example 5 70 91.3 7.0 91.1 9.8 34.1 Example 6 80 90.9 4.8 90.1 7.5 34.6 Comparative 0 90.6 13.8 90.4 16.8 26.4 Example 1 Comparative 100 89.4 25.3 86.4 34.7 56.1 Example 2 Comparative 70 89.1 29.2 86.8 37.9 41.5 Example 3 Comparative 70 88.8 28.4 86.9 39.8 38.7 Example 4 Comparative 60 90.1 14.7 89.9 24.0 62.8 Example 5 Comparative 70 90.6 13.5 90.1 20.8 63.7 Example 6

According to the present invention, a plastic container can be obtained which is flexible and is superior in impact strength at low temperatures and which causes a small decrease in transparency and do not get very sticky even when it is subjected to heat treatment. 

1. A plastic container having a wall comprising a layer made of a composition comprising from 70 to 99 parts by weight of a crystalline propylene-ethylene-butene-1 copolymer having features [1] and [2] defined below and from 1 to 30 parts by weight of an ethylene-α-olefin copolymer having features [3], [4]and [5], where the combined amount of both copolymers is 100 parts by weight: [1] to have a content of propylene-derived structural units of from 70 to 97% by weight, a content of ethylene-derived structural units of from 1 to 10% by weight and a content of butene-1-derived structural units of from 2 to 20% by weight, [2] to have a melt flow rate, measured at a temperature of 230° C. and a load of 2.16 kgf, of from 1 to 10 g/10 min, [3] to be a copolymer of ethylene and an α-olefin having from 4 to 12 carbon atoms, the copolymer having a content of ethylene-derived structural units of 50% by weight or more, [4] to have a melt flow rate, measured at a temperature of 190° C. and a load of 2.16 kgf, of from 0.1 to 50 g/10 min, and [5] to have a density of from 865 to 898 kg/m³.
 2. The container according to claim 1, wherein the propylene-ethylene-butene-1 copolymer satisfies formula (1) defined below: x+1<y  (1) wherein x denotes a content (% by weight) of ethylene-derived structural units and y denotes a content (% by weight) of butene-1-derived structural units.
 3. The container according to claim 1 or 2, wherein the wall is composed of a single layer made of the composition.
 4. The container according to claim 1 or 2, wherein the wall is composed of two or more layers including at least one layer made of the composition.
 5. The container according to claim 1 or 2, wherein the container is obtained by extrusion blow molding.
 6. The container according to claim 1 or 2, wherein the container is a container for medical use. 